Hi,I also never wired a duct smoke detector but A my friend suggest me for the wiring of the smoke detector,so Determine the smoke detector's input voltage. The fire alarm system's control panel, located near the air handler, lists the smoke detector's input voltage and labels the control system's wire terminals. Usually two sets of wires extend from the management panel's wire terminals. One set leads to the smoke detector's input power supply and the other leads to the smoke detector's alarm circuit. In some cases, the smoke detector receives its input power from the air handler. Check the control panel's wiring diagram to verify the input power's source.so may it prove helpful for you.thanks
if this is a commercial unit. the power will come from the fire panel and also have a battery back up. I have never seen power supplied form any other source. The battery back up should maintain a charge for at least 90 minutes in the event of power loss.